A vacuum countergravity casting process using a gas permeable mold is described in such prior patents as the Chandley et al U.S. Pat. Nos. 4,340,108 issued July 20, 1982, and 4,606,396 issued Aug. 19, 1986. That countergravity casting process involves providing a mold having a porous, gas permeable upper mold member (cope) and a lower mold member (drag) engaged together, sealing the bottom lip of a peripheral wall of a vacuum chamber to the mold such that the vacuum chamber confronts the gas permeable upper mold member, submerging the bottom side of the lower mold member in an underlying molten metal pool and evacuating the chamber to draw the molten metal through one or more ingate passages in the lower mold member and into one or more mold cavities formed between the upper and lower mold members.
The Voss U.S. Pat. No. 4,616,691 issued Oct. 14, 1986, discloses sealing the bottom lip of a peripheral wall of a vacuum chamber to a mold using a reusable elastomeric sealing gasket carried on the bottom lip. During casting when the mold is immersed in an underlying molten metal pool, the elastomeric sealing gasket is thermally insulated, conduction wise, from the heat of the underlying molten metal pool by the mold-forming material of the drag and shielded from the radiant heat of the molten metal pool by a skirt depending from the peripheral wall of the vacuum chamber. The sealing gasket is insulated, conduction wise, from the pool by a substantially thickened upstanding ridge or shoulder formed on the drag and is sealed to the mold at a site atop the mold which is thermally remote from the molten metal pool.
It is an object of the present invention to provide an improved vacuum countergravity casting apparatus and process wherein a vacuum chamber includes a cooled, thermally conductive peripheral wall having a lower end sealed to the mold by an elastomeric sealing gasket engaged therebetween and wherein cooling of the thermally conductive peripheral wall maintains the sealing gasket at a temperature where thermal degradation thereof is reduced during casting, thereby prolonging the useful life of the sealing gasket in the casting of successive molds.